Conventionally, an amorphous transformer using an amorphous alloy as the material of the iron core is known. In this amorphous transformer, amorphous alloy foil bands are laminated and bent in a U-shape, and both ends of the amorphous alloy foil bands are butted or overlapped to provide a wound iron core, and the iron loss can be smaller than that of transformers using conventional electromagnetic steel sheets.
However, in the wound iron core structure, stress to worsen the magnetic properties occurs when the material is bent. Therefore, it is necessary to subject the iron core to annealing treatment in a magnetic field to release the stress in order to improve the above magnetic properties. By performing annealing treatment, recrystallization starts inside the material to lead to embrittlement. This applies not only to amorphous alloys but also to electromagnetic steel sheets. At this time, the annealing conditions have a connection with the composition of the alloy, and for Metglas® 2605SA1 of a conventional material, annealing is performed at a temperature of more than 330° C. for 30 minutes or more. Also, in Patent Document 1, the annealing conditions are decided using an original formula.
Patent Document 1: JP-A-58-34162